Diffuse injury to microvasculature of the lung produces a proteinaceous exudate within the pulmonary interstitium and alveolar space. Injured cells release tissue thromboplastins which activate the clotting system generating a diffuse extravascular fibrin matrix within the lung. This clot-matrix contains fibronectin, a 220,000 dalton subunit glycoprotein which participates in diverse biological processes, including cell adhesion and matrix organization. Fibronectin is covalently linked to the Alpha chain of fibrin by plasma factor XIII during clot formation and a fibrin/fibronectin network is identified associated with hyaline membranes and with the surface of pulmonary alveolar macrophages during acute lung injury. We plan to investigate the interactions of macrophages with matrix fibrin and fibronectin in vitro and in a hyperoxic guinea pig model of acute pulmonary injury. We will examine mechanisms of macrophage binding to fibronectin using radiolabelled fibrin and fibronectin in complex forms. Anti-A6F10, a monoclonal antibody which blocks human monocyte binding to fibronectin-coated surfaces, is present on human and guinea pig mononuclear phagocytes and on the U937 histiocytic cell line. We will determine the factors which alter the expression of cell surface A6F10 and test the effects of A6F10 modulation on monocyte binding to fibronectin/fibrin matrices, phagocytosis, and platelet interactions. We have identified the presence of a plasma Factor XIII antigen on the macrophage surface. The ability of Factor XIII to cross-link fibrin, fibronectin and collagens suggests a possible new mode of interaction between macrophage and the clotting system. The molecular weight of this antigen will be determined by immunoprecipitation from radioiodinated and S35 label macrophages. Stimuli which modulate cell-surface Factor XIII in vitro will be ascertained and its ability to transglutaminate fibrin, and fibronectin examined. We will investigate the in vivo role of the fibronectin in pulmonary repair using a hyperoxic guinea pig model of diffuse lung injury and fibrosis. Alterations in the distribution of matrix proteins and inflammatory cells induced by alveolar damage will be evaluated in tissue, bronchoalveolar lavage and plasma. Western blotting will be used to identify proteolytic fragments and complexes of fibronectin in vivo which may have biological function.